A process of forming a film such as a nitride film on a substrate is often performed by alternately supplying a precursor and a reactant such as a nitriding agent to the substrate. The nitride film has excellent insulating properties, corrosion resistance, dielectric properties, film stress controllability and the like, and has been widely used as an insulating film, a mask film, a charge storage film, a stress control film of semiconductor devices. It is also used as various etch stops, but there is also a demand for reducing thickness with the miniaturization of transistors. There is a trade-off relationship between the thinning and etching resistance. In order to improve the etching resistance, a method is also known in which chlorine which will be an impurity is reduced by supplying a plasma-excited hydrogen gas while alternately supplying the precursor and the reactant.
In the above method, however, although the chlorine concentration within a film may be reduced in a low temperature region, it may be difficult to reduce the hydrogen concentration within the film.